1. Field of the Invention
This invention relates generally to oscillating systems and more particularly to a method and circuit which produces rapid initiation of the rise time in the output of an oscillator.
2. Description of the Prior Art
Desirable characteristics for an oscillator in a projectile fuzing system are starting the oscillator pulse rapidly so that its initial amplitude is a substantial portion of its final amplitude and having its starting phase controlled by a modulating pulse, so that it is immune from external interfering signals. Advantages of a projectile fuzing system with these characteristics include lessening the effect external counter-measure signals have on the fuze, increasing fuze performance, improving system sensitivity, and range cut off performance.
A prior fast rise time oscillator, described in U.S. Pat. No. 3,849,741, issued to Groom, III et al. on Nov. 19, 1974 uses a transient, generated within the oscillator transistor by stored charge depletion during the modulating pulse, causing rapid oscillation build-up. The oscillator circuit includes a transistor which initially has one of its junctions in a forward biased condition, and which then is caused to operate in a normal transistor mode which reverse-biases the junction to produce an internal transient caused by the quick turn-off time of the junction. However, there are several disadvantages to using this system. While pulse build-up is relatively fast, it still requires several rf cycles (about 400 MHz) and does not exploit the full potential of stored-charge depletion (step-recovery) devices. Additionally, this transient performance is an incidental property of the oscillator transistor, not defined by any recognized specification. Finally, it is not wise to tie together in one device both step-recovery and oscillator performance requirements.